Source Code VB

Introduction

            With this tutorial you can learn how to code the MCI Device via the Mci Command String Interface. I will not give you much specific code but show you how to write your OWN code to suit your needs. That way you will learn how to program using the MCI Command String Interface. The MCI Interface is fairly powerful and can be very useful. You can play almost any movie file available. Including DVD Movie’s (If you have a Video Card that has hardware support for dvd playback), Play Divx Movie’s(Must have the Divx Codec installed), AVI movies, QuickTime movies and more. Can also play a wide range of music files including MP3, WAVE, MIDI, and more. In this tutorial I will show you how to program the Mci Device so you would be able to make a feature rich media player. As for the exercise in this tutorial I will show you how to make a music player with a few features. If I get good response’s and feedback I may create another tuturial in the future. I am pretty sure though, after you read and study this tutorial you will be able to create your own music and movie player with ease.

Note: I didn’t go through by over my writing with a fine toothed comb. So, there could be some mistakes.

———————————————————————————————–

Lets get some Documentation

            Start out by going to (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/multimed/mmcmdstr_85uz.asp) website and look over some of the documented MCISendString Commands available. For example: Click on the open command at the left side of the webpage. Scroll down alittle on the right side of the page and you will see the documented device types and the device flags available for that device type.. Scroll down alittle more and it will explain what the meaning of each device flag is for. For example: Find the waveaudio device. Look at the column to the right and you will see the available flags that will work with the waveaudio device. Find the buffer buffer_size flag. Scroll down  to the Value section of the page and find the buffer buffer_size flag and look to the right and it explains what it is for and what it does. So, now that we’ve got that lets get started with programming the Mci Device.

            Note: The mpegvideo device driver is not documented at the msdn webpage. We can still do quite alot with it since alot of the commands from the digitalvideo device and waveaudio device will work with the mpegvideo device. The MpegVideo device type would be the Device Driver of choice for all of our multi-media needs since it will play alot of the movie and music formats out there.

———————————————————————————————–

Whats that mciSendString thing?

            The first step you will want to do is add

Private Declare Function mciSendString Lib “winmm.dll” Alias “mciSendStringA” (ByVal lpstrCommand As String, ByVal lpstrReturnString As String, ByVal uReturnLength As Long, ByVal hwndCallback As Long) As Long - to the declarations section of our form. The return value of the mciSendString function will be a number. It will return different numbers for different errors or return a 0 if the command was successful. Example: Say we made a variable Dim Error as long - We would use our mciSendString function in this manner. Error = mciSendString(”Open ” & Filename & ” alias movie”,0,0,0) - Error would contain a number returned by our Mci Device to let us know what happened. More on that below. I will briefly go over each parameter of the mciSendString function.

           

            The lpstrCommand parameter is a string that specifys the MCI command string and flag. In other words this parameter would be our command that we pass to the MCI Device. Like in our paragraph above, open would be a command string that we passed to the MCI Device. It tells the MCI Device to do something. The command string could also have flags associated with it. More on that below in the tutorial.

           

            The lpstrReturnString parameter is a buffer that receives the return information. Example: If we used the status command string and used the position flag, lpstrReturnString would contain the position information of the music or movie we are playing. We would just create a string variable with a character buffer. Example: Dim ReturnData as String * 128. We would put ReturnData in the parameter and it will contain our position value.

           

            The uReturnLength parameter is the size, in characters of the lpstrReturnString parameter. If we used Dim ReturnData as String * 128 for our lpstrReturnString parameter. Then the size we would put for the uReturnLength parameter would be 128 or you can put Len(ReturnData).

           

            The hwndCallback parameter you will most likely never use. It would contain the Handle to to a callback window if the Notify flag was used in our command string. Just set this parameter to 0.

 

Note: If the command string does not return a value in the lpstrReturnString parameter then you can set the lpstrReturnString, uReturnLength, hwndCallback parameter to “0″. More on that further in the tutorial.

———————————————————————————————–

Whats that mciGetErrorString thing?

            The second step you would want to do is add

Private Declare Function mciGetErrorString Lib “winmm.dll” Alias “mciGetErrorStringA” (ByVal dwError As Long, ByVal lpstrBuffer As String, ByVal uLength As Long) As Long - to the declarations of the form. This is a very useful function for programming the Mci Device. This will convert the number returned by our Error variable into something that we will be able to understand alittle more. It will give us a brief description of what happened. I will briefly go over each parameter in this function.

           

            The dwError parameter will receive our return value from our mciSendString function.

Example: Say we used Error as our variable to receive the return value of our mciSendString function. In the dwError parameter we would put our Error variable.

           

            The lpstrBuffer parameter will contain the string value of our dwError parameter. Example: Say we had Dim GetError as String * 128. If you put GetError in this parameter then GetError would receive the error string.

           

            The uLength parameter is the character length of the dwError parameter.

Example: Say we used the above GetError string variable. We would create the string to have a buffer of 128 characters. Dim GetError as String * 128. So, in the uLength parameter we would put 128 or you can put Len(GetError). Either way will work just fine. ———————————————————————————————–

Write our Music Player

 

            Let start doing alittle MCI Programming by making a simple mp3/wave player. Put 4 command buttons, 3 labels, and a timer on the form. With the first command button name it cmdPlay set the caption to “Play”, the second name cmdStop set the caption to “Stop”, the third name it cmdPause set the caption to “Pause”, the fourth name cmdClose and set the caption to “Close”; name one of the labels lblPosition and will be used for the position status, name the second label lblLength and will be used for the length, and the third name lblError will be used to give us our Mci error status(Make the label fairly big because our error could have a long explanation). The timer will give the position status of the music every second, so set the interval to 1000.

            Pretty much always the first step in programming the Mci Device is starting with the open command string, since it is where we select the device type we want to use and create the alias we want to use. So go to the webpage I stated at the beginning of the tutorial and find open and click on it to read the documentation. Look over our available flags. We will want to use 2 of the flags. The type device_type* and alias device_alias* flag. The next step you want to do is select the file you want to play. One annoying thing about the Mci Device is that it has a hard time with long filenames so, you will either have convert the filepath and name to the shortpath of the file or a easier and recommended way is just putting quotes around your filepath and name. The way to do this is first select the file you want to play. Then type wrap the filepath and name in quotes.

Example: Filename = Chr$(34) & “C:\MP3 Music\mysound.mp3″ & Chr$(34). That will wrap the filepath in quotations. Ok, so now that we have selected the file we want to play and put the quotes around the path, lets start programming the Mci Device. Put this in the declarations section of our form.

 

            Dim Filename as string ‘Will contain our file to play

            Dim Error as long ‘Will store our return value from the mciSendString function.

            Dim ReturnData as String * 128 ‘This variable will contain the data from the lpstrReturnString parameter. It will have a 128 character buffer.

            Dim ErrorString as String * 128 ‘Will store our return string from the mciGetErrorString function. With a buffer of 128 characters.

            Dim ErrorSuccess as boolean’ Will contain True or False if our mciGetErrorString was successful at determining our error returned from the mciSendString function

           

            In the cmdPlay button put:

 

Filename = Chr$(34) & “C:\MP3 Music\mysound.mp3″ & Chr$(34). ‘Replace the path ‘and filename with one that you have.

Error = mciSendString(”open ” & Filename & ” type mpegvideo alias oursong”,0,0,0)

 

O.k. Lets break this down. Our Error variable will contain the return value of the mciSendString command. The open command will open our Filename using the mpegvideo device type and create a alias named oursong.

 

*Note: The type flag can be optional. The Mci Device is usually very good about selecting the correct device driver of our specified file.

*Note: The alias flag can also be optional. I recommend using it so you don’t have to keep referring to your file by the Filename variable. Just use oursong to refer to our opened device.

 

            To see if the Mci Device was successful let call our mciGetErrorString function. In the same command button below the code we already put in add:

ErrorSuccess = mciGetErrorString(Error,ErrorString,12

 

O.k. Lets break this down. Our ErrorSuccess variable will contain the return boolean value of our mciGetErrorString function. It will contain either “True” if it was successful or “False” if it was not successful. The Error variable we used contains the return value from our mciSendString function.

 

            Lets get the description of our error if one was created. In the same command button type in:

lblError.caption = “Error Status: ” & ErrorString

 

Run the program and press the “Play” button. lblError should read “The Specified Command Was Carried Out.” That means that everything went smooth and is O.K.

 

            Now goto the webpage again and find the close command string. In the cmdClose button type:

Error = mciSendString(”close oursong”,0,0,0)

ErrorSuccess = mciGetErrorString(Error,ErrorString,12

 

O.k. Lets break this down. You should already know what the Error variable returns. So, I won’t go over that again.  What the close command does is close either a specified device identifier(Alias) or you can close all device identifiers(Alias’s) by using the all flag. So, what we just told the Mci Device to do is close our oursong device from memory. Notice that the other 3 parameters are “0″? Well, since the close command does not return anything we can just set the parameters to “0″. You should already know what the mciSendErrorString does so I won’t go over that again.

 

            Now run the program again and press the play button twice. lblError should now read “The specified alias is already being used in this application. Use a unique alias.” The error string  returned should be self-explanatory, but I will explain it briefly. What its saying is that the oursong alias is already opened and is being used so if we wanted to open another Mci Device we need to supply a new alias. Now press the cmdClose button. lblError should now read that “The Specified Command Was Carried Out.” That means that our close command was successful at closing our oursong from memory. Now press the play button and lblError should read “The Specified Command Was Carried Out.” Press the play button again and lblError should read that “The specified alias is already being used in this application. Use a unique alias.” If you press that “Close” button lblError should read that the command was carried through. If you press that “Play” button lblError should again read that the command was carried through. O.k. enough of that stuff.

            Now lets program the Mci Device to play our Mp3, Wave, ect. song. Go to the webpage and select the play command and look over it. Every device type reconizes the play command string. In the “Play” button between the mciSendString code and the mciGetErrorString code that we already put their type:

Error = mciSendString(”play oursong”,0,0,0)

            O.k. Let break this down. The play command tells the Mci Device to start playing oursong. Pretty simple. Run the program and press the “Play” button and it should start playing the song you specified in the Filename variable. Everything should be going well. If it isn’t check the lblError caption and see what the mciGetErrorString function is returning. Maybe while you was looking at the documentation on the play command you noticed a from position flag and a to position flag. What these 2 flags do is allow you to start playing at a certain point in the file and play to a specified point in the file. If you want to play the complete file then just ignore these 2 flags. But if you want to specify a starting point and a ending point you would program the Mci Device in this manner.

Error = mciSendString(”play oursong from ” & 1000 & ” to ” & 3000,0,0,0)

            O.k. Lets break this down. We told the Mci Device to play oursong from “1000 milliseconds” to “3000″. Pretty simple right? Now that we have a play command and a close command, what if you just wanted to stop the song at its current playing position and not completely close the file? Well, thats where the stop command comes in. Go to the msdn website and click on the close command. Notice that their is only 1 flag avilable and thats for digital devices? Their are no other flags we need for this command. Lets write our stop command. In the cmdStop button type:

 

Error = mciSendString(”stop oursong”,0,0,0)

 

            O.k. Lets break this down. Not much to break down. Its pretty self-explanitory. What it will do is tell the Mci Device to stop playing oursong. Not really anything more to say.

            What if you wanted to add a pause command to our music player? Nothing to it. Just go to our Mci documentation website and click on the pause command. Pretty much like our stop command it doesn’t have any special flags associated with it. Lets write our pause command. In the cmdPause button type:

 

Error = mciSendString(”pause oursong”,0,0,0)

 

            O.k. Lets break this down. The pause command is simply telling the Mci Device to stop playing oursong at the current playing position. Pretty simple. What if you wanted to resume a song that you paused with the pause command? Nothing to it. Just go to the website and click on the resume command and look at the documentation. Just like our pause command their are no special flags associated with the resume command. Put another command button on the form and name it cmdResume and set the caption to “Resume”. Lets write our code to resume the playing of oursong.

 

Error = mciSendString(”resume oursong”,0,0,0)

 

            O.k. Lets break this down. It is just simply telling our Mci Device to resume playing from where it was paused at when we used our pause command. Nothing to it huh?

            O.k. Now you have some basic functionality for your music player. Now you may want to be able to track the current position that the music is currently playing at. No Problem. Go to our documentation website and click on the status command string. Look around on that page you see a ton of flags available with this command string. If you look at the waveaudio device you will see a position flag. That is the one we want to use to get the current position of our song. Lets write some code for it. In the timer control put:

 

Error = mciSendString(”status oursong position”,ReturnData,128,0)

lblPosition.Caption = “Position: ” & Val(ReturnData)

 

            O.k. Lets break this down. you should already know what the Error variable is for. The status command is telling the Mci Device that we want to get the status of oursong. But to use the status command we have to specify a flag. So, you will have to tell the Mci Device what status information to return. We specified the position flag so, it will return the current playing position of oursong. lblPosition will contain the position value. Noticed that I used Val(ReturnData) for the lblPosition caption? I did it so that lblPosition will only contain the numbers in the ReturnData string. Getting the hang of it now? Lets get our Mci Device to do more. Did you happen to wonder what time format the position flag was in? Well, lets have the Mci Device tell us what the answer is. Looking at our documentation webpage you should still be at the status command string documentation. Look under either the digital video or waveaudio device type. You will see that their is a time format flag. That is the flag that we will use to get the current time format the Mci Device is using. Just draw a command button on the form and name it cmdTimeFormat set the caption to “Time Format”. In the code window of that button type:

 

Error = mciSendString(”status oursong time format”,ReturnData,128,0)

Msgbox ReturnData

 

            O.k. Lets break this down. We are passing the status command string to the Mci Device and using the time format flag. This will tell the Mci Device to give us the current time format. We will get our answer by getting the value of our ReturnData variable. If you want you can just open the Mci Device by pressing the “Play” button and then press the “Time Format” command button. It will send a messagebox with the time format that the Mci Device is currently using. It most likely should say “milliseconds”. Still with me? Easier then you thought huh? What if you wanted the format in seconds? Well, the Mci Device doesn’t support returning the time format in seconds but you can easily do it yourself. 1000 milliseconds = 1 second. So, all you would need to do it create a variable to divide our ReturnData / 1000. The variable will contain the value in seconds. What if you wanted to get the length of the song? Well, that is just as easy as getting the position. in the “Play” command button right above our mciGetErrorString function type:

 

Error = mciSendString(”status oursong length”,ReturnData,128,0)

lblLength.Caption = Val(ReturnData)

 

O.k. Lets break this down. We are simply telling our Mci Device to tell us the length of oursong. Earlier we asked the Mci Device to give us the current time format and it returned “milliseconds”. So, that will be the format that our length will be returned in since we haven’t changed the time format. Can we change the time format? Yeps we sure can. Go to our Mci document page and click on the set command string. Just like our status command string the set command string has a few flags available to use. The flag we want to use to change the time format would be none other then the one of the available time format flags. What you will find out though is some files like mp3 the Mci Device only supports the “milliseconds” time format. If we use the mpegvideo device driver then the only available time formats would be “frames” and “milliseconds. Since we are playing music files we won’t be able to get a time format in “frames”, only “milliseconds”. If you only wanted to play wave files, for example, you could use the waveaudio device type and get the time format in “bytes”, “milliseconds”, and “samples” I don’t think “milliseconds” is all that bad though. What else would you want to add to your music player? Want to know if the music is currently playing? Would you like to be able to change the position of the file in real time? How about a volume control? Want all 3? Well, lets get started and first write a simple function let our application know if it is playing or not. Write the code below in the form.

 

Private Function playingStatus() as boolean

            Error = mciSendString(”status oursong mode”,ReturnData,128,0)

            If Left(ReturnData, 7) = “playing” then

                        playingStatus = True

            Else

                        playingStatus = False

            End If

End Function

 

            O.k. Lets break this down. We are going to use our playingStatus function to contain “True” or “False” depending on whether or not the Mci Device is playing. If you check out our documentation website and clicked the status command string. Then scrolled down you would find a mode flag available. If you read the description of the mode flag it tells you what value’s it would return. So, now to get the playing status we would just need to get the value that is stored in our ReturnData variable. But since our ReturnData variable is 128 characters long we only want to get the first 7 characters. If ReturnData contains “playing”(which is 7 characters long) then our Mci Device is currently playing and will put “True” in our playingStatus function. Other modes are avilable too. The device can return “stopped”, “paused”, “not ready”, ect. Right now we are only interested in checking our Mci Device to see if it is “playing” or not. Thats important for our changing the position code. Lets write that now. Put a Hscrollbar control on our form and name it posChange. Type this code in the “posChange_scroll” sub:

 

            Dim TheSec as long’ Will convert our value of seconds to milliseconds

 

            TheSec = posChange.Value * 1000 ‘TheSec will contain the value in “milliseconds”

            If playingStatus = True then

                        Error = mciSendString (”play oursong from ” & TheSec, 0, 0, 0) ‘ The Mci Device is playing so play from

            else

                        Error = mciSendString (”seek song to ” & TheSec, 0, 0, 0) ‘ TheMci Device is not playing so seek to

            end if

 

            O.k. Lets break this down. If you go to our documentation webpage and click on the play command string you will see a available flag named from. That is the command string and flag we will use to keep the file playing but at a position specified by our TheSec variable. If you go to our documentation website and clicked on the seek command string you will find a available flag named to. That is the command string and flag that we will use to move the position and but not start playing. Got that? We made the variable TheSec for the reason explained below. To recap what I said above if oursong is already “playing” we will want to continue “playing” oursong but at the point in the file specified by our TheSec variable. So we will use the command string play and use the flag from to continue playing oursong “from” the position specified by our TheSec variable. Enough about that already. Lets move on. The Hscrollbar cannot contain a value larger than “32767″. Since the time format of the Mci Device is in “milliseconds” and the total length of almost every song would be larger then “32767 milliseconds” we must convert the “milliseconds” format to a smaller number. The useful and easy thing to do would be to convert it to “seconds”. So, we will set the .Max property of our Hscrollbar to equal the total length of the song in “seconds”. To do this. Let go back to the cmdPlay button and type this code below our code that tells the Mci Device to “play”.

           

            Error = mciSendString(”status oursong length”,ReturnData,128,0)

            posChange.Max = Val(ReturnData) / 1000 ‘This will convert our “millisecond” value to a value in “seconds”

            ‘Remember that 1000 milliseconds will equal 1 second. 2000 milliseconds = 2 seconds and so on.

 

            O.k. This should be fairly simple to understand. We are just telling the Mci Device to return the length of oursong. posChange.Max property will now contain the length in seconds. We divided the number returned by our ReturnData variable by 1000 which would equal “seconds”. Got that? I hope so. Now if you go back and look at the code above to change the position you should understand it alittle more. TheSec variable will contain the posChange.Value value and multiply it by 1000 so our Mci Device will be able to read it properly. “milliseconds” instead of “seconds”. I hope this helped you instead of confused you. If you have any problems don’t hesitate to let me know. I’m trying to thoroughly explain it so you will completely understand. Just as a reminder. If the code is not doing what you expected and you want to find out what is going on use the mciGetErrorString function. O.k. Enough on this. Lets do one last thing that would be useful for a music player. Let create a volume control. Put a Vscrollbar control on the form and name it volScroll and set the .Max value to “1000″. “1000″ is the max for the volume. “0″ is the minimum. Then go to our documentation webpage and click on the setaudio command string.  Look over the available flags and you will find a volume to flag. That is the command string and flag we will want to use. So in the volScroll_Change sub put in this code.

 

            Error = mciSendString(”setaudio oursong volume to ” & volScroll.Value,0,0,0)

           

            O.k. This should be pretty simple to understand. We are simple telling our Mci Device to set the volume of oursong to the current value of the volScroll control.

 

Conclusion

 

I hope this tutorial we went over gave you a nice understanding of how to program the Windows Mci Device. As you can see there are quite a few commands and flags available to do almost anything you want in a Movie or Music player. You could “turn of the left audio channel”, “set the volume for the right audio channel”, “you could open and close the cd door”, “change the speed at which the movie or music plays at” and much more.You should be able to decide what features you want and program the Mci Device to do it for you. Remember to use the mciGetErrorString function as it is very useful. It tells you if the device understood what you told it to do, if the Device Type that you are using supports that command string, and much more. Bookmark the msdn webpage I gave you(http://msdn.microsoft.com/library/default.asp?url=/library/en-us/multimed/mmcmdstr_85uz.asp) so you can have it as a good reference to see what command strings and flags are available. If you found this tutorial useful please vote and leave feedback. You can contact me at: elitecobra@hotmail.com and check out my webpage at: www16.brinkster.com/codesource. Until next time.

Happy Coding